You can clone with
HTTPS or Subversion.
I have tried this and not sure where to put it in Style.css?
This is an open issue because this feature has not been added to Display Posts Shortcode yet. Once it is added, you will be able to use this parameter in the shortcode.
There is no pro version of Display Posts Shortcode. Once I have some free time I will be adding this feature to the plugin.
My guess is that you left the opening <?php tag when it wasn't needed (ex: php was already open).
You really shouldn't be adding code to your functions.php file if you don't understand it and can't modify it for your own needs.
Added in 03886da